The present invention relates to a boiling water reactor (BWR) and an acoustic damping method for a boiling water reactor, and more particularly to reliably monitoring and controlling pressure oscillation generated in a main steam line. The present invention also relates to a monitoring method for a boiling water reactor and a storage medium having stored thereon a computer program for monitoring a boiling water reactor.
As one reason for causing pressure oscillation in a main steam line of a boiling water reactor, pressure oscillation caused by acoustic resonance can be considered. In other words, in the main steam line extending from a steam dome of the reactor pressure vessel to a high pressure turbine through a steam pipe, a pressure wave generates due to variations in the flow rate of steam fluid. The generated pressure wave is propagated and reflected within a steam line including the steam pipe. This creates a standing wave (acoustic resonance mode) having large amplitude, and the amplitude of the pressure oscillation may increase, i.e., resonance vibration may occur. Especially, in a power plant where the power generation capacity is increased, since variations in the flow rate of steam become larger due to increased flow rate of steam, a large acoustic resonance often occurs. Such acoustic resonance phenomenon is subject to the pipe arrangement and boundary conditions of the power plant, and therefore every power plant has different vibration characteristics. It is thus difficult to predict frequency, amplitude, and the maximum amplitude of the vibration caused by acoustic resonance.
Therefore, in order to ensure the soundness of the main steam line and other equipment, it is necessary to design the main steam line and the equipment to have sufficient design margin. For this reason, various measures, such as optimizing the flow passage shape for the main steam line and increasing the structural strength of the main stream line, are taken to prevent the pipes and valves in the main steam line or the equipment from being damaged by an increase in pressure oscillation caused by acoustic resonance. These case examples and measures were reported, for example, by Non-patent literature document 1 (NRC SPECIAL INSPECTION REPORT, 50-265/03-11).
Further, Non-patent literature document 2 (Journal of Engineering for Gas Turbines and Power, April 2004, Vol. 126 P. 271-275) also discloses using Helmholtz resonators in the field of thermal power generation for damping acoustic oscillation within the gas turbine combustor.
However, according to the prior art as described above, carryover of moisture that is mixed and carried with steam is measured when a steam dryer is damaged due to acoustic resonance. If the carryover takes a value equal to or higher than the threshold value because of some sort of malfunction in the steam dryer, the operation of the boiling water reactor is stopped. Namely, the boiling water reactor is not particularly provided with any interlock mechanism which can prevent damage to the steam dryer. There has been existed a method for measuring fluctuating pressure, acceleration and strain at the main steam line when the output power of the nuclear power plant is increased, and for stopping the operation of the boiling water reactor based on the results of measurements. However, there is no particular measure for preventing damage of the steam dryer. Further, if the main steam line is designed to have sufficient design margin to prevent damage caused by pressure oscillation caused by acoustic resonance, the equipment cost of the power plant increases in the end. Further, although there is known a method for attenuating acoustic oscillation within the gas turbine combustor using Helmholtz resonators, such a method is not applied or practiced to the usage of Helmholtz resonators for restricting pressure oscillation in the main steam line of the boiling water reactor.
In other words, conventionally, there has been no particular method for monitoring and controlling pressure oscillation in the main steam line in order to prevent damage of the steam dryer in the reactor pressure vessel. If an attempt is made to restrict pressure oscillation, upon increase in the pressure oscillation, by decreasing the flow rate of steam that is generated in the reactor, the operating rate and the generated energy of the power plant will be decreased, leading to a difficulty in obtaining desired electric power output.
In view of the above, the present invention seeks to provide a boiling water reactor and an acoustic damping method for the boiling water reactor, which can efficiently restrict pressure oscillation caused by acoustic resonance generated in the main steam line and prevent the steam dryer, etc. in the reactor pressure vessel from being damaged, without increasing the equipment cost of the power plant or lowering the thermal power of the reactor.
The present invention also seeks to provide a monitoring method and a storage medium having stored thereon a computer program for monitoring a boiling water reactor, which can prevent the steam dryer, etc. in the reactor pressure vessel from being damaged by pressure oscillation caused by acoustic resonance generated in the main steam line.